The last time I blogged about the eMR2 I’d just parked it in the garage after more smoke escaped as I was jockeying it into the tight confines of my driveway. Opening up the case, it was glaringly obvious that a couple of capacitors had cracked open. Not knowing anything about the internal architecture of the Siemens inverter, I’m lucky there are people who have the skills to repair inverters far more broken than mine and the generosity to share their knowledge on the web.
Rudolf Bosnjak from Bosnia resurrected an original VW CityStromer EV by reverse engineering the broken parts without any technical help from Siemens. Unfortunately, his page seems to disappear every once in while so try again in a few weeks if it doesn’t work for you. According to him, these capacitors are part of the DC-DC converter though they’re also mighty close to a 300A fuse that would only be relevant on the power side of the electronics. They must have not failed completely as the DC-DC converter still appeared to work after the smoke but maybe they were just not quite completely broken yet.
There must have been around thirty screws that required removal before the board could be eased out from under a thick busbar foot that made sliding out the circuit board far more difficult than it should have been. I’m guessing the inverter innards are assembled and then dropped into the box as a unit.
After cross-referencing the out-of-date part number with the current number, with a little help from my friend Jim with his nicer-soldering-iron-than-mine (and soldering skills to match), the old capacitors were unsoldered, the board carefully cleaned of all the ooze and the new capacitors soldered in place.
Despite a battery pack that can only handle a few miles on a good day, the eMR2 drove noticeably better than before the fix. There was no cogging on regen and no fault-outs like I’d come to expect when flooring it at low SOC. The inverter actually compensated for conditions that used to require a restart, it’s been a long time since I haven’t had to preoccupy myself with temperamental electronics. I ran the car up and down the alley just enjoying the smooth ride and the cool breeze through the windows. We’re back in business!